The present invention relates to an optical reproducing device, which projects a light beam onto an optical memory medium such as a magneto-optical disk which uses the magnetic ultra high resolution method, and which controls the quantity of light of the light beam so as to bring close to a predetermined value the quantity of a reproducing signal from recorded marks, and to an optical memory medium for use therein.
Recent years have seen prolific development of high-density recording by means of magneto-optical disks which use the magnetic ultra high resolution method, provided with a recording layer and a reproducing layer. In magneto-optical disks of this type, a light beam is projected onto the reproducing layer of the disk, and in an area of the reproducing layer within the light beam spot which is heated to above a predetermined temperature (hereinafter referred to as the xe2x80x9caperturexe2x80x9d), the magnetization of the recording layer is copied to the reproducing layer. Thus recorded marks smaller in diameter than the light beam spot can be reproduced.
In devices for reproducing magneto-optical disks of this type, even if the driving current for producing the light beam is held constant, there are cases in which the reproducing power of the light beam fluctuates with changes in the ambient temperature at the time of reproducing. If reproducing power is too strong, the aperture becomes too large, which increases crosstalk from reproducing signals from adjacent tracks, and reading errors occur. Again, if reproducing power is too weak, reproducing signal output from the target track is reduced, and again reading errors occur.
In a xe2x80x9cRecording and Reproducing Device for Magneto-Optical Memory Medium and Magneto-Optical Memory Mediumxe2x80x9d disclosed in Japanese Unexamined Patent Publication No. 8-63817/1996 (Tokukaihei 8-63817) (U.S. Pat. No. 5,617,400), the aperture is maintained at a fixed size, and accurate data reproducing is performed, by reproducing a control pattern of repeated long marks and repeated short marks on a magneto-optical disk, and controlling reproducing light quantity so as to bring close to a predetermined value a ratio of the reproducing signal quantities of the two types of marks.
FIG. 11 explains the general structure of a magneto-optical disk reproducing device according to the foregoing conventional art. When projected light fxe2x80x2 from a semiconductor laser 202 is projected onto a magneto-optical disk 212, reflected light gxe2x80x2 from recorded marks for reproducing power control on the magneto-optical disk 212 is converted into a reproducing signal axe2x80x2 by a photodiode 203. The reproducing signal axe2x80x2 is sent to an A/D (Analog/Digital) converter 205 and to a clock producing circuit 204. By means of PLL (Phase Locked Loop), the clock producing circuit 204 produces a clock signal cxe2x80x2 synchronized with the reproducing signal axe2x80x2. Then, in accordance with the clock signal cxe2x80x2, the A/D converter 205 converts the reproducing signal axe2x80x2 into digital data dxe2x80x2. On the basis of the digital data dxe2x80x2 sampled according to the clock signal cxe2x80x2, an amplitude ratio detecting circuit 213 calculates and outputs a ratio between an amplitude of the reproducing signal axe2x80x2 of the long marks and an amplitude of the recording signal axe2x80x2 of the short marks (amplitude ratio rxe2x80x2). A differential amplifier 210 then compares the amplitude ratio rxe2x80x2 with a standard value, producing a difference exe2x80x2 therebetween. A reproducing light quantity control circuit 211 then outputs a driving current ixe2x80x2 for the semiconductor laser 202 in such a way that feedback reduces the difference exe2x80x2, thus controlling the driving current ixe2x80x2 of the laser light in such a manner that an optimum reproducing light quantity is always applied.
However, in calculating the amplitude of the reproducing signal axe2x80x2 from each type of mark, the amplitude ratio detecting circuit 213 calculates the amplitude based on digital data dxe2x80x2 sampled at a single upper peak position and digital data dxe2x80x2 sampled at a single lower peak position. Accordingly, it is difficult to improve the precision of the amplitude, and the precision of the amplitude ratio rxe2x80x2 calculated from the respective amplitudes may also be impaired. This results in the problem that accurate control of reproducing light quantity is difficult.
Here, sufficiently precise control of the reproducing light quantity is particularly necessary when using the foregoing magnetic ultra high resolution magneto-optical disks, because of their high recording density. Again, since the short marks are set to be shorter than the long marks, the reproducing signal axe2x80x2 from the short marks has a smaller amplitude, and fluctuates with a shorter cycle, than the reproducing signal axe2x80x2 from the long marks. Consequently, it is particularly difficult to improve the precision of the amplitude of the short marks.
It is an object of the present invention to provide an optical reproducing device and an optical memory medium which are capable of precisely detecting the amplitude of a reproducing signal from recorded marks.
In order to attain the foregoing object, an optical reproducing device according to the present invention includes a reproducing signal producing section, which outputs a reproducing signal obtained from recorded marks recorded in an optical memory medium; a signal quantity detecting section, which samples the reproducing signal at indicated sampling points, and outputs a reproducing signal quantity; a timing producing section, which indicates to the signal quantity detecting section sampling points having a phase offset from peak positions of the reproducing signal; and an amplitude calculating section, which, based on a plurality of the reproducing signal quantities, outputs an amplitude signal showing the amplitude of the reproducing signal.
With the foregoing structure, the reproducing signal from the recorded marks is sampled with a phase offset from peak positions of the reproducing signal, and the amplitude calculating section outputs an amplitude signal based on a plurality of reproducing signal quantities. Accordingly, an amplitude signal can be produced more precisely than when an amplitude signal is produced on the basis of reproducing signal quantities sampled from a reproducing signal only at peak positions within each period thereof.
Further, since the sampling points are not limited to peak positions, the timing producing section can indicate sampling points (for example at shoulder portions of the reproducing signal) with a timing suited to production of the amplitude signal. Accordingly, precision of the amplitude signal can be improved even in comparison with a case of averaging a plurality of reproducing signal quantities sampled only at peak positions.
In addition, in order to improve the precision of the amplitude signal, it is preferable to produce the amplitude signal based on reproducing signal quantities obtained from a plurality of periods of the reproducing signal, or to make more samplings per period of the recorded marks.
In addition to the foregoing structure, it is preferable if the sampling points indicated by the timing producing section are sampling points offset to precede upper or lower peak positions of the reproducing signal, and sampling points offset to follow upper or lower peak positions of the reproducing signal.
With this structure, even if the phase indicated by the timing producing section for use as the sampling points differs somewhat from the most suitable sampling points, the variation in the preceding and following sampling points creates fluctuations in the amplitude signal in mutually opposite directions, which thus cancel each other out. Consequently, even if the instructions of the timing producing section include error, the amplitude calculating section can produce a precise amplitude signal. Moreover, if the preceding and following sampling points are set an equal interval from the upper or lower peak positions, fluctuations in the amplitude signal due to variation in the preceding and following sampling points will also be substantially equal, thus further improving precision.
Incidentally, the peak positions on which the preceding and following sampling points are based may mutually differ; for example, the preceding sampling points may precede upper peak positions while the following sampling points follow lower peak positions. In such a case, precision of the amplitude signal can be improved without much increase in power consumption. Moreover, if sampling points are set preceding and following each peak position, the number of sampling points per period of the recorded marks can be increased, thus further improving precision of the amplitude signal.
In addition, the timing producing section may indicate sampling points with a frequency of four times the frequency of the recorded marks. In this case, the timing producing section can indicate sampling points by means of a periodic clock signal, and accordingly circuit structure of the timing producing section and the reproducing signal producing section can be simplified. Further, since there are no unnecessary reproducing signal quantities even if sampling is performed in synchronization with a clock signal, circuit structure of the amplitude calculating section can be made simpler than in a case where the reproducing signal producing section outputs unnecessary reproducing signal quantities.
Further, in addition to the foregoing structures, it is preferable to provide the optical reproducing device with a control section, which, on the basis of the amplitude signal, controls light quantity of a light beam projected onto the optical memory medium during reproducing of data therefrom by the reproducing signal producing section. With this structure, since the control section controls the light quantity of the light beam on the basis of a precise amplitude signal, the light quantity can be controlled precisely, and errors during reproducing can be decreased.
In addition, if the timing producing section is able to indicate sampling points with a phase differing from the peak positions of the reproducing signal of the recorded marks, the timing producing section may determine the timing from the reproducing signal of the recorded marks. In this case, in particular, sampling points may be indicated without changing the optical memory medium. Alternatively, the timing producing section may determine the timing from clock marks previously recorded in the optical memory medium. In this case, circuit structure of the timing producing section can be made simpler than in a case where the timing producing section independently determines sampling points.
An optical memory medium according to the present invention is for use in an optical reproducing device which, on the basis of values sampled from a reproducing signal from recorded marks recorded in the optical memory medium, controls a reproducing light quantity during reproducing, and, in order to attain the foregoing object, includes a control domain, in which the recorded marks are recorded; and clock marks which express a timing, differing from peak positions of the reproducing signal from the recorded marks, at which sampling is to be performed by the optical reproducing device.
In the optical memory medium with the foregoing structure, the clock marks are previously recorded. Accordingly, the optical memory medium can indicate sampling points to the optical reproducing device more precisely than when the optical reproducing device independently detects sampling points. Consequently, the precision of the amplitude signal calculated by the optical reproducing device can be further improved.
The foregoing optical memory medium may be manufactured by simultaneously forming the clock marks and the recorded marks therein, or by previously forming clock marks therein, and then, while confirming the phase of the clock marks, forming the recorded marks therein.
In addition, it is preferable if the frequency of the clock marks is set to four times the frequency of the recorded marks. With this structure, only necessary sampling points are indicated, and the number of clock marks can be reduced. Further, since even an optical reproducing device of simple structure can detect the amplitude value with precision, the size of the control domain can be reduced. Consequently, the efficiency of use of the optical memory medium can be improved.
Incidentally, the foregoing optical reproducing device and optical memory medium are particularly suitable for use as an optical reproducing device and an optical memory medium which are expected to precisely detect the amplitude of the reproducing signal from the recorded marks. Examples of these are an optical memory medium which includes a recording layer, in which the recorded marks are magnetically recorded, and a reproducing layer laminated thereon, in which projection of a predetermined light beam forms an aperture within which recorded marks are copied to the reproducing layer, and an optical reproducing device for such an optical memory medium.
Additional objects, features, and strengths of the present invention will be made clear by the description below. Further, the advantages of the present invention will be evident from the following explanation in reference to the drawings.